Field of the Invention
The present invention relates to wireless communication and, more particularly, to a cell reselection method and a user equipment using the method.
Related Art
3GPP (3rd Generation Partnership Project) LTE (long term evolution) which is improvement of UMTS (Universal Mobile Telecommunications System) has been introduced as 3GPP release 8. The 3GPP LTE uses OFDMA (orthogonal frequency division multiple access) in a downlink, and uses SC-FDMA (Single Carrier-frequency division multiple access) in an uplink. The 3GPP LTE adopts MIMO (multiple input multiple output) having maximum four antennas. Recently, a discussion of 3GPP LTE-A (LTE-Advanced) which is the evolution of the 3GPP LTE is in progress.
Meanwhile, in the 3GPP system, handover refers to the process of transferring a user equipment in communication in a current cell to another cell, and cell reselection refers to the process of transferring a user equipment in idle state in a current cell to another cell.
However, depending on situations, cell reselection may be repeated with a very short period. For example, handover of a user equipment may take place back and forth (ping-pong) between two cells. Many attempts have been made to avoid the ping-pong phenomenon. However, since the cell reselection process of a user equipment in idle state starts by measuring a cell, a lot of previous attempts failed to completely solve the ping-pong phenomenon.